With increases in speed and performance of semiconductor devices, the electric energy needed for semiconductor elements is also on the rise. Combined with the trend toward smaller size and higher integration of semiconductor elements, the increase in electric energy needed for semiconductor elements leads to an increase in heat generated per unit area. As a result, semiconductor elements are prone to malfunction due to thermal runaway, to thereby hinder the increase in function and performance of electric system apparatuses incorporating such semiconductor devices.
As a way to solve the problem with semiconductor elements, there has been considered a method of effectively transferring heat generated in the semiconductor element to a radiating plate through a thermally conductive material. Specifically, the semiconductor element and the radiating plate cannot be directly coupled due to constraints of electric circuits, and hence development has been carried out on a semiconductor device including a semiconductor element and a radiating plate bonded to each other through a thermally conductive insulating material. In the development, electrode is thickness increased with respect to the substrate used in power electronics for the purpose of increasing current density and reducing the size of the substrate, with the result that breakdown voltage is reduced or the electrode is delaminated, making it difficult to ensure both an insulating properties and reliability.
To address the above-mentioned problem, as illustrated in FIG. 18, there has been proposed a semiconductor device in which a coating film is formed around an electrode placed above a ceramic substrate through a bonding layer (see, for example, Patent Document 1). This semiconductor device is produced by combining the ceramic substrate and the electrode through the bonding layer and then forming the coating film around the electrode.    Patent Document 1: JP 2005-116602 A